Predetermined temperature coefficient capacitor

Abstract

A screen printed capacitor to provide a predetermined temperature coefficient of capacitance. The capacitance device utilizes a common electrode with a uniform dielectric layer in conjunction with two side-by-side base electrodes resulting in opposite polarity temperature coefficient of capacitance values. The proportion of the area of each of the side-by-side base electrodes with respect to each other determines the predetermined temperature coefficient of capacitance required.

What is claimed is: 
     
       1. A thick film capacitor with a predetermined fixed temperature coefficient of capacitance, said capacitor comprising: a substrate;   a first layer of at least two separate electrodes of different materials positioned side by side in the same layer plane, said two separate electrodes being physically in contact with each other;   a dielectric layer fired on said two separate electrodes; and   a top layer electrode formed over said dielectric, the effects of said dielectric layer being fired over said two separate electrodes providing in conjunction with said top layer electrode a negative temperature coefficient of capacitance with one of said two separate electrodes and a positive temperature coefficient of capacitance with the other of said two separate electrodes, said two separate electrodes operating in conjunction with said top layer electrode to provide a capacitor with said predetermined temperature coefficient of capacitance.   
     
     
       2. A thick film capacitor as defined in claim 1 wherein said two separate electrodes are screened onto said substrate in an area inversely proportional to the ratio of the temperature coefficient of capacitance of each electrode. 
     
     
       3. A thick film capacitor as defined in claim 1 wherein said predetermined temperature coefficient of capacitance is one of a postive, negative or zero temperature coefficient of capacitance. 
     
     
       4. A thick film capacitor as defined in claim 1 wherein said substrate is alumina. 
     
     
       5. A thick film capacitor as defined in claim 1 wherein said one of said two separate electrodes contain silica and said dielectric comprises Bi 2  O 3  ·TiO 2 . 
     
     
       6. A thick film capacitor as defined in claim 1 wherein said other of said two separate electrodes is silica free. 
     
     
       7. A method of making a thick film capacitive device with a predetermined coefficient of capacitance comprising the steps of: screen printing a first base electrode with a specific material composition on a substrate;   screen printing a second base electrode with a different material composition than said specific material composition in said first base electrode on said substrate in side by side contact with said first base electrode;   firing said first and second base electrodes;   screen printing a uniform dielectric layer over said first and second base electrodes;   firing said dielectric layer to produce an electrochemical effect not only between said first base electrode and said dielectric layer but also between said second base electrode and said dielectric layer;   screen printing a common electrode over said uniform dielectric layer so that said electrochemical effect between said first base electrode and said dielectric layer producing in operational conjunction with a common electrode a negative temperature coefficient of capacitance and so that said electrochemical effect between said second base electrode and said dielectric layer producing in operational conjunction with said common electrode a positive temperature coefficient of capacitance; and   firing said common electrode.   
     
     
       8. A method of making a thick film capacitor device as defined in claim 7 and additionally comprising the step of tailoring the top conductor layer over one of said first and second base electrodes to provide a precise value of temperature coefficient of capacitance of said capacitor.